Angular rate sensors are used to measure the rotational velocity of an object without a fix point for referencing. A Micro-Electro-Mechanical System (MEMS) angular rate sensor (or MEMS gyro) can be incorporated into mobile devices due to its small size, weight and low cost. The principle of operation is based on the Coriolis effect. A MEMS resonator is driven at a certain frequency (e.g., about 10 kHz). Due to the angular rate the Coriolis force excites a second oscillation perpendicular to the first one. This oscillation is proportional to the angular rate and can be measured using capacitive methods. Application examples include but are not limited to: image stabilisation (e.g., in cameras or mobile phones); input devices for virtual reality applications; platform stabilisation; sensors for game consoles; and sensors for navigation systems.
The MEMS gyro is susceptible to bias, scale factor errors, and axis cross-sensitivities, as well as high frequency noise. Cross-axis sensitivity is strongly affected by mounting stresses, while the magnitudes of the bias and scale factor errors are related to external temperature. For example, changes in gyro bias are approximately linear to changes in external temperature. To mitigate the effects of gyro bias, the gyro bias can be estimated using known mathematical formulations and subtracted from the raw gyro data. Calibration using measurements at known angular rates can be used to determine the cross-axis sensitivity. Unfortunately, constraints on processing speed, power and memory can make these mathematical formulations impracticable for applications running on mobile devices with limited resources.